Location: Aquatic Animal Health Research2012 Annual Report
1a. Objectives (from AD-416):
The overall objective of this project is to define the nutritional value and nutrient bioavailability of various protein and oil sources to improve feed formulations, decrease feed costs for channel catfish and tilapia and increase the use of U.S. agricultural products/byproducts. Efficient feeding practices to improve fish performance and health will be developed for improved formulations. Objective 1: Determine the nutritional value and nutrient bioavailability of various protein sources (especially distillers' dried grains with solubles (DDGS)) and essential fatty acids and their effects on growth, feed palatability, stress, immune response and disease resistance. Objective 3: Develop feeds and feeding strategies to improve nutrient retention, production efficiency, product quality and fish health.
1b. Approach (from AD-416):
The U.S. aquaculture industry faces numerous challenges including high feed and energy costs, low-cost imports and lower fish prices paid to producers. Among these, feed cost represents the largest expenditure in aquaculture operations, and protein is the most expensive component in fish feeds. Lower cost alternative protein sources to replace fish meal and other expensive protein sources must be identified. Soybean meal (SBM), because of its low-cost, availability, consistent quality, and high nutritional value, is the most commonly used plant ingredient in fish feeds, comprising up to 45% grow-out diets. Distillers' dried grains with solubles (DDGS) is readily available and less expensive than SBM and other conventional protein sources on a protein-cost basis, but its use in fish feeds is very limited. Replacement of SBM or more costly ingredients by DDGS would reduce feed costs. This proposed project will investigate the nutritional value and nutrient bioavailability of DDGS derived from various grain sources, and corn DDGS from ethanol plants for channel catfish and tilapia, define the essential fatty acid (EFA) requirement, optimum ratio of n-3 to n-6 and their effect on gene and protein expression, identify biologically active compounds in DDGS which may improve fish growth and health, and develop least-cost feed and feeding strategies to improve nutrient retention, product quality and health. This project should lead to reduced feed costs, increased use of DDGS, and improved feeding practices which will lead to improved growth and survival and product quality, lower producton costs, as well as increased demand of DDGS.
3. Progress Report:
A 10-weeks feeding study to determine the essential fatty acid (EFA) requirement of male hybrid tilapia was conducted using a control diet with 6% coconut oil (diet 1) and nine test diets containing different levels and proportions of linoleic acid (LA, n-6) linolenic acid (LN, n-3). Fish fed the control diet deficient in LA and LN had the poorest growth and feed efficiency (FE). Similar performance was obtained in fish fed other diets. Analysis of whole body lipid showed that tilapia accumulated higher levels of n-6 than n-3 as the body ratios of n-6 to n-3 were higher than dietary ratios. Dietary treatments had no effect on hematological and immunological parameters and the resistance of fish to bacterial (Streptococcus (S.) iniae) infection. This study indicates that both LA and LN are dietary essential for juvenile hybrid tilapia. However, compared to LN, LA appears to have a better growth promoting effect. Dietary LA alone can meet the EFA requirement of hybrid, and a level of 1.14% of diet is required for optimum growth. Another 10-week study evaluated the nutritional value of distiller's dried grains with solubles (DDGS) from various sources (3 corn DDGS, 1, 2, and 3, 1 whiskey DDGS, 1 sorghum DDGS and 1 wheat DDGS) as replacements of one-third of protein supplied by soybean meal + corn meal. Fish fed diets containing corn DDGS 2 and 3 had significantly higher weight gain than those fed the control diet and diets containing corn DDGS 1, sorghum DDGS and wheat DDGS. This variable did not differ among fish fed other diets. This growth improvement was due to improved feed intakes since FE did not differ among all treatments. The source of dietary DDGS has no influence on hematological variables, serum immune responses and the resistance of fish to S. iniae infection challenge. Another study evaluating the nutritional value of different fractions of by-products from ethanol distillery [DDGS, distiller's dried grains (DDG), distiller's solubles (DS) and DDG + DS] as replacement of one-third of protein supplied by soybean meal + corn meal was conducted with channel catfish. Preliminary results showed that feed consumption was essentially the same for all diets but fish fed diets with DS or DDG + DS had better weight gain and FE than fish fed other diets. The differences, however, were not always significant. Fish fed diets containing distillery by-products appeared to have more resistance to the Flavobacterium columnare challenge. A similar study with all-male tilapia hybrid is currently on-going.
1. Dietary essential fatty acids to improve growth and health of all-male hybrid tilapia. Published information indicates that tilapia have a dietary requirement for linoleic (LA, n-6) series fatty acids (FAs). The optimum levels of n-6 FAs reported were 0.5% and 1% for redbelly and Nile tilapia, respectively. It has been reported that linolenic (LN, n-3) series FAs are also dietary essential for tilapia, but the requirement levels of n-3 and its growth promoting effect relative to n-6 are unknown. A study to evaluate the effects of various levels of dietary LA, LN or their combination on growth, body FA composition, hematology, immune response and resistance of all-male hybrid tilapia to Streptococcus (S.) iniae challenge was conducted by ARS researchers in Auburn, AL. Results showed that fish fed the control diet lacking of both LA and LN had the lowest weight gain (WG). Fish fed diet with 1.0% LA had the highest weight gain (WG), but did not differ from fish fed diets with 0.5 or 2.0% LA and 0.26, 0.40, 0.69, 0.25, 0.50 and 1.0% LA in combination with 0.5, 1.0, 2.0, 0.25, 0.5, and 1.0 LN, respectively. Feed intake, feed efficiency (FE) and survival were similar among fish in all treatments. Body FA content is generally a reflection of dietary FA. Total n-6 FAs increased with increasing dietary levels of n-6. There was also a trend of increasing body n-3 content with increasing dietary levels of n-3, but the values peaked at a dietary level of 1%. Tilapia accumulated higher levels of n-6 than n-3 as the body ratios of n-6 to n-3 greatly increased relative to dietary ratios. Dietary treatments had no effect on hematological and immunological parameters and the resistance of fish to S.iniae infection. This study indicates that both LA and LN are essential for growth of juvenile tilapia hybrid. Compared to LN, LA appears to have a better growth promoting effect and an LA level of 1.14% in diet is recommended for maximum growth of hybrid tilapia.
2. Distiller's dried grains with solubles (DDGS) is a lower cost alternative ingredient in fish feeds but their nutritional value varies among DDGS sources. DDGS, a by-product resulting from the fermentation of grains for the production of alcohol for beverage or fuel, has been found as a good alternative protein in fish feeds. Earlier studies by ARS researchers in Auburn, AL, show that feed cost was substantially reduced without adverse affect on fish performance and health by replacing soy meal with 30% corn or wheat DDGS. Physical and chemical characteristics and nutritional value of DDGS vary with the grain source and quality as well as between and within ethanol plants due to fermentation time and efficiency and the drying process. A study to evaluate the effects of DDGS sources (corn DDGS from 3 ethanol plants, and a whiskey DDGS, wheat DDGS and sorghum DDGS) as replacements of one-third protein from soy meal on growth, feed efficiency (FE) and resistance of all-male tilapia hybrid to Streptococcus (S.) iniae challenge, shows that color, smell, proximate nutrient content and nutritional value of DDGS varied among sources. Diets containing corn DDGS 2 and corn DDGS 3 that had bright yellow color and sweet alcohol smell provided significantly better weight gain than the control diet and diets containing corn DDGS 1,sorghum DDGS and wheat DDGS. However, diets containing DDGS performed equally well or better than the control diet. This growth improvement was due to improved feed intakes since FE was similar among all diets. The source of DDGS used has no effect on hematology, serum immune responses and the resistance of fish to S. iniae infection. DDGS from various sources can be used to replace one-third of protein from soy meal without affecting hybrid tilapia performance and health. Fish performance can be significantly enhanced by selecting DDGS with bright and light coloration, and sweet, fresh alcohol odor.Lim, C.E., Li, E., Klesius, P.H. 2011. Distillers dried grains with solubles as alternative protein source in diets of tilapia. Aquaculture. 3:172-178.